Aim: To evaluate the expression of leptin and leptin receptor in benign prostatic hyperplasia (BPH) and prostate cancer (Pca), and to investigate whether they are associated with the development and progression of Pca. Methods:Immunohistochemical staining was performed to examine the expression of leptin and leptin receptor in BPH and Pca.Pca was divided into three groups: localized Pca, locally advanced Pca and metastatic Pca. The positive staining was identified and the percentage of the positive staining was graded. We also assessed the relationship between both the Gleason score and body mass index (BMI) and Pca. Results: The percentage of the leptin expression in Pca was significantly higher than that in BPH (P < 0.01). For the Pca group, the expressed levels of leptin showed a considerable correlation with localized Pca and metastatic Pca (P < 0.05). Leptin receptor, however, did not reveal a definite difference between BPH and Pca. The expression of leptin indicated a significant difference between well-differen-tiated Pca (Gleason score < 6) and poorly differentiated Pca (Gleason score 8-10) (P < 0.05), The relation between the leptin expression level in Pca and the BMI was not remarkable (P = 0.447). Conclusion: Our results suggest that leptin might have a promoting effect on the carcinogenesis and progression of Pca.